The overall quality of platelets for transfusion is not considered satisfactory by most workers in the field. The problem is due partly to the inherent difficulty of collecting and storing these highly reactive cells, and partly to the lack of adequate in vitro assay methods. The techniques available in modern cell biology have not been applied fully to this problem (a major conference on this subject will be held in April 1991). It is well established that platelets undergo a sequence of contractile and motile events when stimulated by a variety of activating agents. Our laboratory has shown that platelets stored under blood banking conditions for transfusion purposes exhibit morphological changes including the formation of bizarre or aberrant morphologies. Consistent with these observations, we have demonstrated in other studies that conditions of storage of platelets caused changes in the composition of the platelet cytoskeleton. Under normal conditions of platelet activation with physiological agonists, actin-rich microfilaments and the microtubules are rapidly and extensively reorganized. Alterations of the cytoskeletal network in stored platelets include the association of additional actin-binding proteins with the microfilaments, and most notably, the direct association of tubulin with actin. We have available several very sensitive methods for identifying storage-induced changes In the platelet membrane, the membrane skeleton (cytoskeletal proteins closely associated with the membrane), and the cytoskeletal proteins. Characterization of protein patterns has been achieved by one- and two-dimensional SDS-polyacrylamide gel electrophoresis under both non-reducing and reducing conditions. Identification of proteins is performed by immunoblotting using a variety of monoclonal antibodies to actin, myosin, actin-binding protein and tubulin and antibodies to membrane glycoproteins Ib, IIb, IIIa and the IIb/IIIa complex. We have recently acquired an antibody which is directed towards a glycoprotein expressed on the surface of activated platelets (anti-PADGEM, platelet activation dependent granule-external membrane protein) which will serve as a sensitive probe of the activation state of stored platelets. We plan to use this antibody in both immunoblots of membrane proteins and in a flow cytometric analysis of platelets stored under various conditions. We will correlate the activation state data with morphological alterations by phase microscopy and the immunochemical analyses.